264 PALEONTOLOGY OF NEW YORK. 



Test thin, marked by numerous fine concentric striae, which at irreguhir 

 intervals have been raised into iinbrifatintr ]aniolla\ loavinff stronir varices 

 on the cast. 



Interior unknown. 



A specimen has a length ol' -yl mm. and bright '!■> nmi. 



Tliis species is distinguished from M. Chemungensis by its straighter foi-in, 

 erect beaks, and convexity along the medial line. 



Formation and locality. In the Yellow sandstones, at Burlington. Iowa. 



Mytil.'\rc.\ fibristriata. 



PLATE XXXHI, KIGS. 6, 7 ; AND PLATE LXXJCVU, FI«. H. 



Mytilus jihrUtriatiix, White and Whitfield. Prnc. Boston Soc. Nat. Hist., vol. viii, p. 296. Kd,., 1SC2. 

 " WhnfiehUann.t. Wi.vcuell. Proc. Acad. Nat. Sci., Phila., p. 413. Sept., 1862. 



p. 11. 1S63. 

 Mytilarca fibristriata, (W. .-iiid W.). Hali,. Prolim. Notice, L.im. Shells, etc., pt. 2. p. 24. 1869. 



" JihH.itriafa (W. and W.) {fimhristriata. in error), Hai.i,. Pal. N. T.. vol. v, jit. 1. Plates and 



Kxplanatinn.'s : PI. 33. fi^'S. 6, 7. .Inn., 1883. 



Shell of medium size; body very elongate, luirrow elliptical; length more 

 than twice the height ; byssal area convex and inflated : ventral margin 

 nearly straight for two-thirds the length, thence curving into the abruptly 

 rounded posterior extremity ; dorsal margin very gently curved to the 

 extremity of the hinge-line. 



Valves equal, moderately convex in the posterior part, becoming gibbous 

 in the middle and anterior. 



Hinge-line short, oblique. Beaks narrow, sub-erect, rmbonnl region 

 narrowly gibbous. 



Test thin, marked liy fine, tiiread-like, uudidatiug radii, whii-h are 

 more or less interrupted ly the fine concentric stria?. 



Interior unknown. 



A specimen has a length of 48 mm., and height 'I'l nun. 



This species is distinguished from M. occidmtalis by its lesser gibbosity ; the 

 convexity of the body is along the ventral side instead of the median line ; 

 and by the presence of undulating, filamentous radii. 



Formation and locality. In the Yellow sandstones at Burlington. lo\va. 



